Perovskite synthesis route

Various metal and metal oxide nanoparticles have been prepared on polymer (sacrificial) templates, with the polymers subsequently removed. Synthesis of nanoparticles inside mesoporus materials such as MCM-41 is an illustrative template synthesis route. In this method, ions adsorbed into the pores can subsequently be oxidized or reduced to nanoparticulate materials (oxides or metals). Such composite materials are particularly attractive as supported catalysts. A classical example of the technique is deposition of 10 nm particles of NiO inside the pore structure of MCM-41 by impregnating the mesoporus material with an aqueous solution of nickel citrate followed by calicination of the composite at 450°C in air [68]. Successful synthesis of nanosized perovskites (ABO3) and spinels (AB2O4), such as LaMnOs and CuMn204, of high surface area have been demonstrated using a porous silica template [69]. 

Buffat, P. Perret, D. Xanthopoulos, N. Bucheli, O. (2005). Characterization of Perovskite Powders for Cathode and Oxygen Membranes Made by Different Synthesis Routes. Jowmal of the European Ceramic Society, Vol. 25, No.l2, (March 2005), pp. 1991-1995, ISSN 0955-2219... 

Perovskites AB)/3C2/303 (A = Ba, Sr, B = Zn, Mg, Co, Ni C = Nb, Ta) are promising compounds for microwave applications. It is important to synthesize these complex oxides as pure perovskite phases because the slightest admixture of a second phase hinders drastically the dielectric properties of ceramics, which sinter only at very high temperatures (1400 to 1500°Q. The precursor chemistry resembles greatly that of BaTi03 formation by alkoxide or alkoxide-hydroxide routes. Below we summarize the 3 approaches to the synthesis of these perovskites by the sol-gel method ... 

Recently, the synthesis of truly triple and quadraple perovskites has been reported in the literature by way of metathesis reactions. The low temperatures routes are necessary to realize the formation of otherwise meta-stable phases. Articles describing the utility of topotactic methods for the synthesis of several perovskite and related phases can be found elsewhere. ... 

The best precursors are obtained using the sol-gel technique for they require lower calcination temperatures, allow better microstructural and compositional control plus the flexibility to produce a variety of shapes. Chandler et al. (1993) have reviewed the chemical aspects of solution routes to produce mixed oxides. The thermal decomposition of heterobinuclear complexes reported by Skaribas et al. (1991) leads to the production of perovskite oxides. More recently, Moreau et al. (1996) synthesized binuclear complexes of La-Ni, La-Co and La—Cu. Upon calcination at 973 K, the former two complexes yielded LaNiC>3 and LaCoC>3 perovskites while the latter yielded La2CuC>4. The main limitation in this and related methods is the complicated synthesis of the binuclear complexes that makes their application for large scale processing very unlikely. 

YBa2Cu307 (T 9Q K). We knew the structure had to be that of a defect perovskite from the beginning, because of the route we adopted for the synthesis. 

For some applications, such as in multiferroic materials based devices, it is the crystal symmetry of the multiferroic what matters. In these materials the presence or not of a centre of symmetry is crucial for the observation of ferroelectricity. With this regard, there are cases, as in some AMnOs perovskites (A=Y or Dy), in which the synthetic route determines whether an orthorhombic compound with a centre of symmetry (i.e. non ferroelectric) or a hexagonal phase without the centre (i.e. ferroelectric) is formed (Carp et al., 2003 Dho et al., 2004). Consequently, preparative conditions have to be carefully selected in order to obtain crystal phases with the adequate structure. The use of more than one synthesis method is thus worth trying in all cases. 

---